Sorry guys for not replying sooner. I appreciate all of the comments and I will try to answer the questions.
I didn't think the numbers were correct but I figured the temp difference was what was needed. What should be the difference between the out and in at the owb? We just had a cold front come through. I've been burning seasoned locust and it has improved my burn times some, but I'm still not getting more than 10 hours when the temperature is below 35 degrees.
I am going to try to follow Hondas recommendation and try to get a more accurate reading. It would be difficult to take the hx out so I would rather not try that.
How would I go about checking for the air bubble?
Regarding the filters...I change those about every month.
I have their thermopex buried about 20" deep. The dirt has settled so water lays in the ditch at times (new construction so no grass seed planted there yet).
Linda...The 2000 ft does not include the basement but I would like to add that in the future only turning the unit on when I'm down there.
If I sell, what do used (1 year old) units usually sell for? Brand new before taxes is $5000.